NY Times used data from Strava to write the article, and there are other sources as well. Like this study from 2017:
A Comparison of the Energetic Cost of Running in Marathon Racing Shoes
> Conclusion
> The prototype shoes lowered the energetic cost of running by 4% on average. We predict that with these shoes, top athletes could run substantially faster and achieve the first sub-2-hour marathon.
Not that easy. NYT data shows not only 4% increase for VaporFly, but also 3% increase for Streak.
Springer is harder. Though 18 male aren't enough to prove anything, the data is quite consistent. But 4% equals to 5 min in marathon. That means that a lot of athletes from 2013-14 could break 2 hours in that shoes easily. Probably 5 min on a treadmill at 18 km/h has little in common with 2 hours at 21 km/h.
But he also wore Vaporfly for his 2017 attempt, I thought - I doubt the prototype is 4% on top of that, or even 4% compared to what top-class runners were wearing before.
He did, but that was at Monza with more turns, maybe more elevation difference, not as good drafting strategy, etc. He said he learned a lot from that, so who knows how fast he would run if he had made another attempt in the exact same conditions but with the added experience.
At Monza he ran in 2:00:25 and this race took 1:59:40, that's 0.62% faster. Definitely within reason for a technical improvement.
The pacers wore Vaporfly, Kipchoge wore a prototype. The Vaporfly have been shown to actually make a difference of around 4%.
https://www.nytimes.com/interactive/2018/07/18/upshot/nike-v...